Device for heating preforms provided with supporting ring

ABSTRACT

A device for heating parisons made of a thermoplastic material and having a supporting ring for blow molding hollow bodies, having a conveyor means, a plurality of holding means which are arranged on the conveyor means and grip the head area of the parisons between the supporting ring and the mouth and radiant heaters arranged on the path of movement of the parisons carried by the holding means, a shield supported by the conveying means being assigned to each holding mandrel in the form of a cover plate which is located at the height of the supporting ring and has a borehole to receive the supporting ring. Furthermore, there is also a cooling device, which acts directly on the exposed head area. This permits optimum protection of the head area of the parisons, which is not to be shaped or deformed, to prevent unacceptable heating.

[0001] This invention relates to device according to the preamble ofclaim 1.

[0002] British Patent 2 095 611 B has already disclosed such a devicewith which the parisons are gripped on the outside in the head area bymeans of holding fingers between the supporting ring and the open mouthand the shielding is formed by a cylindrical protective jacket whichsurrounds most of the head area including the supporting ring. Althoughthe parison head area, which is not to be deformed, is protected fromdirect heating by the radiant heater due to this protective jacket, itis not protected from indirect heating by the protective jacket, whichis itself heated by the radiant heaters.

[0003] British Patent 2 095 611 B has already disclosed such a devicewith which the parisons are gripped on the outside in the head area bymeans of holding fingers between the supporting ring and the open mouth,and the shielding is formed by a cylindrical protective jacket whichsurrounds most of the head area including the supporting ring. Althoughthe parison head area, which is not to be deformed, is protected fromdirect heating by the radiant heater due to this protective jacket, itis not protected from indirect heating by the protective jacket, whichis itself heated by the radiant heaters.

[0004] The object of this invention is to improve upon the protection ofthe head area of parisons, which is not to be deformed, to protect itfrom unwanted heating in the case of a generic device. This object isachieved according to this invention by the features characterized inthe characterizing part of claim 1.

[0005] In the case of a device according to this invention, the headarea of the parisons is protected by the cover plates from directheating due to the radiant heaters. In addition, indirect heating viathe closed protective sleeves (not included) is prevented, and insteadan active cooling of the head and thread areas is implemented.

[0006] Advantageous refinements of this invention are characterized inthe subclaims. The design according to claims 3 and 4 is especiallyexpedient. Because of the continuous shielding by the cover plates,which form a type of strip, this makes it possible to heat the area ofthe parisons, which is to be heated especially rapidly and in an energysaving manner in a closed heating channel, and to do so while theparisons are in the normal upright position.

[0007] An exemplary embodiment of the present invention is describedbelow on the basis of drawings, which show:

[0008]FIG. 1 a schematic top view of a device for heating a parison;

[0009]FIG. 2 section A-B according to FIG. 1;

[0010]FIG. 3 a vertical section through a reflector belonging to thedevice according to FIGS. 1 and 2;

[0011]FIG. 4 the detail Z according to FIG. 2 in an enlarged diagram.

[0012] The device 1 according to FIGS. 1 through 4 is set up for heatingparisons 2 made of PET, supplied at room temperature, to the processingtemperature between approximately 90° C. and 110° C., which is requiredfor stretch blow molding. It is integrated into a stretch blow moldingmachine, which is shown only schematically and in part, with a feederstar 13, a transfer star 14 and a blowing wheel 15, where hollow bodiesin the form of beverage bottles are produced from the preheated parisons2 by stretch blow molding.

[0013] The parisons 2, which are closed at the bottom, have a supportingring 3 in their upper area, and the head 5, which is located between theopen mouth 4 and the supporting ring 3, has an external thread and isalready in its final form. The head 5 is not involved in the stretchblow molding operation and therefore must not be heated in any case to atemperature close to the processing temperature in order to avoidunwanted deformation.

[0014] The device 1 has a continuous conveyor chain 12 having aplurality of chain links 12 a of the same type which are joined togetherby pins in an articulated manner and have laterally protrudingprojections 12 b, which revolve in a horizontal plane over a drivingwheel 16 and a deflecting wheel 17. Between the driving wheel 16 and thedeflecting wheel 17, there are two parallel linear revolving regions,which move around the wheels and in which the chain links 12 a areguided precisely by means of stationary rails 19 and rollers 18, whichare mounted on the chain links so they can rotate.

[0015] In at least one of the two linear revolving regions, a pluralityof similar stationary heating boxes 7 are situated on the path ofmovement of the parisons 2, which are carried by the conveyor chain 12,each box being equipped with a plurality of horizontally aligned tubularinfrared lamps 36.

[0016] A sleeve 20 having a vertical rotational axle is mounted in eachprojection 12 b of the conveyor chain 12 and is connected in arotationally fixed manner to a toothed wheel 21; it engages with astationary toothed rack or a continuously revolving roller chain 21 andsets the sleeve 20 in continuous rotation when the conveyor chain 12 isrotating continuously. A holding mandrel 6 is accommodated in eachsleeve 20 in a rotationally fixed manner but with an adjustable height.The holding mandrel projects out of the bottom side of the sleeve 20 andis rigidly connected to a control rod 22 which projects at the upper endof the sleeve 20. A compression spring 23 which presses the holdingmandrel 6 into its upper end position shown in FIGS. 1 and 2 is insertedbetween the broadened end of the control rod 22 and the sleeve 20, thisposition being defined by stops (not shown). With the help of controlrod 22 and stationary curve ramps (not shown), the holding mandrel 6 maybe moved into its lower end position (indicated with a dash-dot line inFIG. 2) against the force of the compression spring 23. This liftingmovement serves to introduce the holding mandrel, which is equipped witha spring ring, into the open mouth 4 of the parison 2 in the area of thefeeder star 13 and for extraction out of the mouth 4 in the area of thetransfer star 14.

[0017] On the lower side of each projection 12 b of the conveyor chain12, a horizontal cover plate 8 having a square periphery is attached ata distance by means of four thin perpendicular rods 11. The cover plate8 consists of an essentially flat piece of sheet metal severalmillimeters thick or a profiled molded part, and it has a centralborehole 9, which is concentric with the sleeve 20 and the holdingmandrel 6. The diameter of the borehole 9 is slightly greater than theoutside diameter of the supporting ring 3. The height and thickness ofthe cover plates 8 are selected so that the supporting ring 3 of aparison 1 is situated centrally in the borehole 9 at a slight distanceof 2 to 3 mm, for example, from the bottom side of the cover plate, andmost of the head 5 projects above the top side of the cover plate 8 andis thus freely accessible from practically all sides between the fourrods when the holding mandrel 6 with the parison 2 placed on it assumesits upper end position (see FIG. 4). In the lower end position, however,there is a parison 2, which is to be gripped or released by the holdingmandrel 6, with its mouth 4 situated at a slight distance beneath thecover plate 8.

[0018] The heating boxes 7, which are arranged in a line on the outsideof the linear peripheral area of the conveyor chain 12, form a linearheating channel K together with plate-shaped ceramic reflectors 35,which are arranged in a line on the inside of the linear revolving area,and a ceramic base plate 26; the parisons 2, which are conveyed in thenormal upright position, project from above with their body area 24which is to be shaped, into the linear heating channel. The heatingchannel K is closed at the upper end by the cover plates 8, which comein contact with one another or are opposite one another at a slightdistance and form a revolving belt of cover plates in combination with alinear cooling shield 27 through which water flows on the side of theheating boxes 7 and a baffle plate 28 on the side of reflectors 25. Thelinear edges of the cooling shield 27 and the baffle plate 28, whichpoint toward one another and run parallel to one another are arranged ata small distance from the cover plates 8 or they come in contact withthe latter. Due to the design of a heating channel K, which is closed onall sides, this permits an extremely effective and energy-saving heatingfor the body area 26, which is to be shaped beneath, the supporting ring3 of the parisons 2.

[0019] To prevent overheating of the surface of the parisons 2, narrowslotted nozzles 29 are provided between the heating boxes 7 with fans 30connected to them, to blow room air in a high concentration onto thesurfaces of the parisons 2 as they revolve past them. Furthermore, acooling fan 31 is connected to the outside of each heating box 7 to coolthe infrared lamps 36. The air which is introduced by the fans 30 and 31into the heating channel K at an excess pressure is removed throughperpendicular slot-shaped orifices 37 provided between the individualreflectors 25. These orifices 37 are either positioned in a singleinclination relative to the direction of emission of the infrared lamps7 a [sic; 36], as shown in FIG. 1, or they are positioned so that thereare two inclinations, as shown in FIG. 3. This prevents the thermalradiation emitted by the infrared lamps 36 from being able to escapedirectly through the orifices 37. The orifices 37 open into a collectingchannel 38 through which the heated air from the heating channel Kcoming from the fans 30, 31 is discharged from the device 1 in acontrolled manner.

[0020] Because of the arrangement described here, the head 5 of eachparison 2 is situated completely outside of the heating channel K and isprotected optimally from direct heating by the infrared lamps 7 a due tothe cover plates 8, which are carried by the conveyor chain 12. Toprevent any indirect heating by heated parts of a device, etc., aseparate cooling system 10 is provided for the heads 5. It has one ormore nozzles 39 which are situated on the inside of the linearperipheral area of the conveyor chain 12 and supply ambient air throughfans 40. If necessary, a heat exchanger 41 which has a coolant flowingthrough it may also be provided in the nozzles 39. Intense cooling ofthe head 5 of the parison 2, which is freely accessible for the mostpart, is achieved by the cooling device 10. In addition, this also coolsthe adjacent parts of the device 1, such as the holding mandrels 6, etc.The air is guided by appropriate baffle plates in countercurrent withthe air flow in the heating channel K and to some extent also throughthe cooling shield 27.

[0021] The cover plates according to this invention can be used in thesame way with parisons in which the supporting ring is not formed on aprojecting neck collar, but instead on a recessed ring groove,especially shaped transition between the head and the body, etc. It isimportant only that the cover plate be arranged at the dividing pointbetween the area of the parison to be shaped further and that which isnot to be shaped further.

[0022] If the parisons are heated in the normal upright position, asshown in this embodiment, the cover plates according to this inventionalso prevent heating of the head area due to hot air ascending out ofthe heating channel. The parisons can therefore be heated with noproblem in a normal position without first rotating them by 180°.

1. A device (1) for heating parisons (2) made of a thermoplasticmaterial for blow molding hollow bodies and having a supporting ring(3), comprising a conveyor means (12), a plurality of holding means (6),which are situated on the conveying means and grip the head area (5) ofthe parisons between the supporting ring and the mouth (4), andcomprising radiant heaters (36) arranged on the path of movement of theparisons which are carried by the holding means, whereby a shield, whichis carried by the conveying means, is provided for each holding mandrelto protect the head area of each parison, which is situated between thesupporting ring and the mouth, from heating, characterized in that eachshield is formed by a cover plate (8), which is arranged at the level ofthe supporting ring (3) is designed with a borehole (9) that surroundsthe supporting ring (3) at a small distance, leaving most of the headarea (5) of the parisons (2) free, and a cooling device (10) which actson the exposed head area (5) of the parison (2) is also provided.
 2. Thedevice according to claim 1, characterized in that each cover plate (8)is designed in the manner of a plate and is connected by at least onerod (11) to the conveyor means (12).
 3. The device according to claim 1or 2, characterized in that the conveyor means are formed by acontinuous conveyor chain (12) having at least one linear revolving areain which the radiant heaters (36) are arranged, and the cover plates (8)have a rectangular or square periphery, and adjacent cover plates (8)contact one another in the linear revolving area of the conveyor chain(12) or they are opposite one another with a slight distance betweenthem.
 4. The device according to claim 3, characterized in that theparisons (2) can be transported in a freely suspended manner in anupright normal position with the mouth facing upward on holding mandrels(6), and with their body area (24) they are immersed in a heatingchannel (K) comprising a radiant heater (36) and diametrically opposedreflectors (25), this heating channel being covered at the top by thecover plates (8).
 5. The device according to claim 4, characterized inthat a plurality of cooling fans (30, 31) are connected to the heatingchannel (K) on the side of the radiant heaters (36), and orifices (37)for removing the cooling air from the heating channel (K) are providedon the side of the reflectors (25).
 6. The device according to one ofclaims 1 to 5, characterized in that the cooling device (10) has atleast one air blowing nozzle (39) directed at the head (5) of theparisons (2).
 7. The device according to claim 6, characterized in thata heat exchanger (41) through which a coolant flows is arranged in theair blowing nozzle (39).
 8. The device according to one of claims 1 to7, characterized in that the holding means are formed by holdingmandrels (6) which are arranged on the conveyor means (12) in such a waythat they are adjustable in height and can be inserted beneath the mouth(4) of the parisons (2).